Power-line signaling



Nava 26, l929 P. H. EVANS 1,736,852

POWERLINE SIGNALING Filed Sept. 24, 1923 2 Sheets-Sheet l Nov,l 26, 1929. P. H. EVANS POWER LINE SIGNALING Filed Sept., 24, 1923 2 Sheets-Sheet 2 Patented Nov.l 26, 1929 UNITED STATES PATENT OFFICE PORTIERE. EVANS, OF WEST ORANGE, NEW JERSEY, ASSIGNOR T AWlilSTIllRJll' ELECTRIC COMPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEW YORK POWER-LINE SIGNALING Application led September 24, 1923. Serial No. 664,432.

This invention relates to communication by means of high frequency waves, and more particularly to communication over power lines by superimposing the high frequency waves'upon the power currents traversing the power line.

Where more than two signaling or tele-4 phone stations are connected to the same high voltage transmission system in such a manner than any station is able to selectively call and communicate with any other station on a high frequency channel, it is desirable that there be some indication at idle stations to show that the signaling channelis busy in order to prevent an attempt at calling while telephone communication is going on. One object of the invention is, therefore, to provide a busy signal at each of the idle stations to indicate when the signaling channel is in use for calling or telephoning.

' When more than two stations are connected' on the same line for communicating over the same high frequency channel or channels and selective means is provided whereby any station may call any other station without ringing the stations not called, it is desirable that arrangements be provided for ordinary code ringing in the manner. of ringing onparty telephone lines be employed. The invention comprises in addition to a selective system whereby each station may call any other station, an emergency key for use when the selective ringing arrangement is not operating satisfactorily for any reason so that upon operation of the emergency key ordinary code ringing may be employed.

l Inasmuch as signaling waves of widely dify fering intensity may be received at a particular station in a system of signaling over power lines, itis advantageous to employ gain control means in connection with each receiver. A further object of the invention is to provide automatic gain control whereby the 'amplification of incoming waves is decreased as a result of the reception of wave energy above the normal volume.

Another object is to provide for connecting signaling apparatus to a power line for transmission thereover by such coupling apparatusas will combine efficient signaling with safety to person communicating by means of the signaling apparatus and with safety to the apparatus itself.

The invention will be best understood, 'both as to the details of its organization and its mode of operation, by referencev to the following description taken in connection .communicate over a high voltage transmission line 3 with other subscribers?ort-operators located at distant points upon the transmission line. At each distant station, vterminal apparatus similar in arrangement` andfunction to thatv illustratedr in the drawing will be provided. By high `voltagetransmission line it is to be understood any system or network of conductors for the electrical transmission of power over which it is possible to transmit high frequency waves. In a particular instance, telephone transmission over a 110,000 volt transmission line hasbeen found toA be practical.

The terminal apparatus illustrated in Fig. 1 comprises, (l) an outgoing channel, and (2) an -incoming channel. The operators telephone set 1 is arranged to -be connected to these channels simultaneously by means of a switch or key 4. In the left-hand position of the switch 4, the signaling channel may be extended by means of a hybrid coil 5 to a cord and plug connection 6 at a telephone switchboard whereby the circuit may be further ,eX- tended to any subscriber or telephone network.

The outgoing channel comprises (l) a high frequency wave generator 7 designed to produce waves at two different high frequencies, for example, 80,000 and 100,000 cycles per second, which will hereinafter be'referred to. as fr uencies f1' and f2 respectively; (2) an ampligying and modulating tube 8 and its assoclated circuits whereby the outgoing waves are modulated in accordance wlth speech; (3) an amplifier 9 and its associated circuits whereby the Waves produced by the osclllator 7 may be amplified to sufficiently high power for transmission under norm'al conditions; (4) an auxiliary amplifier 10 and its associated circuit connections which may be connected into circuit tok increase the power ampliication for transmission under abnormal conditions,` as for example, when a section of the line is-down; (5)x high pass and low pass filters 11 and 12 w ich may be included in the transmission circuit alterna- .tively by means of apparatus hereinafter described; (6) a coupling circuit 13; and (7) coupling capacities 14, the coupling circuit and coupling capacities being common to the incoming and outgoing transmission channels and serving to couple the signaling apparatus with a selected pair of power lin'e'con-` ductors.

The receiving channel extends from the power line through the coupling condensers 14, the'coup'ling clrcuit 13, to the high pass or low pass filter l1 or 12, and includes,I in addition to these elements, (1) high frequency amplifying apparatus 15 for amplifying in one or more stages the incoming waves and (2) a rectifying or detecting tube 16. For calling purposes the incoming channel is normally extended by means of relays through theV circuit of a selector 17, which controls a bell or other signaling device 18.

i The selector 17 is the type of device described and claimed in the patent'to J. C. Field, No. 1,200,095, granted October 3, 1916, and No. 1,343,256, granted June 15, 1920.

For eiiicient signaling it is essential that the signaling circuit be connected with the power line in such a manner as tov effect a suitable transfer of energy from the signaling .cir-- cuit to the line and from the line to the signaling circuit. For protection of the signaling apparatus and persons communicating thereover, itis essential that direct contact with the high voltage lines be avoided The coupling condensers 14 may comprise any suitable4 arrangement whereby a capacity of a suiiiciently large value is provided between the terminals of the signaling circuit:l and the conductors of the power line. Such a capacity may be provided by a fixed condenser adapted to withstand the high voltages or an arrangement of aerial wires arranged ad- 'acent to the power line conductors. It has een proposed to employ a section of high voltage cable, the core of which constitutes the power line conductor and the sheath of which serves Aas a plate of a condenser to which the signaling circuit is connected. However, the manufacture of cable adapted to continuously withstand the high volta es met with is a matter of, considerable di culty. The preferred coupling arrangement consists of a fixed condenser'with either oil or porcelain dielectricor an. antenna arrangement. The coupling circuit comprises condensers 19 and cho e coils20 in series withthe line and condensers 2l and choke coils 22 in shunt to the line. The coils 22 serve also to shunt to ground any cycle current. entering the coupling circuit. Choke coils 23 are connected in the line adjacent the coupling condensers 14. Safety devices comprise fuses 24, open air sparkgaps 25 and 26 of high current capacity and vacuum gaps 27 in shunt to the gaps 26. The vacuum gaps break down quickly under the influence of excessive voltages, and 'thus serve to protect the signaling circuit until Vthe air gaps 26, which are adapted to carry-a much heavier current than the vacuumgaps, come into operation.

'Operation in callz'ngf-The switch 4 is closed at its right-hand contacts, thus connecting the operators setA 1 to the high frequency circuit, closing the contact 30 and opening the contact 31. When the operator miV takes lhis receiver from the switchhook, the Y contact 32 is closed, thereby connecting ground to the conductor 33. 35v and 36 then operate. Since the selector keys SK, SK are normally closed, the operation of the relay 34 closes the contact on the inner armature and thus operates the relay 37. Itwill first be assumed that line conditions are normal and that the auxiliary arnplifier 10 1s not to be used, in which case the relay 35, althoughclosed, performs no function. Under such conditions, the switch 51 is closed in the down position. The relay 36 closes the filament heating circuits of the modulating, generating and amplifying apparatus 8, 7, 9. The operator now actuates one of the keys SK corresponding to the station desired to be called and thus causes the relay 37-to operate each time a tooth of the selector key opens the circuit of the relay 37 thereby placing the condenser 38'into and out of circuit once for each impulse transmitted by the selector keys. Normally the high class filter 11 is connected to the transmitting channel and the low pass lilter 12 is connected to the receiving channel. However, when the relay 34 was operated as aforesaid, the relays 40 and 41 became operated and thus interchanged the high pass and low pass filters so that the low pass filter 12 is connected to the transmitting circuit and the high pass filter 11 is connected to the`receiving circuit. During the operation of the selector key, the frequency generated by the oscillator 7 is thus changed back and forth from the low carrier frequency f1 to the high carrier frequency f2 and vice versa. However, the high carrier frequency is not transmitted to the line inasmuch as the low pass filter is designed to pass The relays 34,

only the low carrier' frequency and to suppress the high carrier frequency. The groups of impulses of the low carrier frequency are thus transmitted to and impressed upon the power line. When the selected station answers, the operator at the calling station may converse bv means of his telephone set and if desired he may 'extend the connection through the hybrid coil 5 and the plug 6 to a telephone switchboard or any subscriber whose line is permanently attached to the plug connection 6. When throwing the switch 4 from the right-hand position to the left-hand position it is essential that the contact 31 be made before the contact 30 is broken in order to hold the ground connection upon the conductor 33 and thus maintain the circuit.

When the `oscillator 7 at the called station transmits high frequency impulses to the line,

relays 42 and 43 at the calling station will not A be operated and the relay 44 willnot be actuated because the. relay 34 remains operated at the calling station thus maintaining the circuit of the relay v44 open at the left-hand contact of the relay 34.l

The station originating a call always.

transmits on the lower of the two carrier frequencies and receives on the higher. v

' Operation at a called station-The electrode circuits of the amplifier 15 and the rectifier-detector 16 are normally energized. Incoming high frequency impulses are rectified bv the rectifier 16. This increases the space current of the rectifier 16 and operates the differential relay 42 inasmuch as vthe outer armature contact of the relay 34 is opened. The 'operation of the relay 42 causesthe operation of the relay 43 thus closing its left-hand contact and connecting the battery through the relay 44 which causes it to operate and supply an impulse of current to the electromagnet of the selector 17 which causes the selector to operate one step. When the incoming oscillations cease, the relays 42, 43 and 44 release which causes an impulse of current of opposite sign through the magnet of the selector 17. A proper series of impulses will cause the selector to close the circuit of the bell 18. At the cessation of the calling impulses the frequency f1 is continuously transmitted to the line, at the calling station and the relays 42 and 43 are maintained operated at the called station. Therefore, when the operator at the called station removes his receiver from the switchhook and places ground upon the conductor 33, thus operating the relay 34, the relays 40, 41 and 37 do not operate because the path to ground through the inner contact of the relay 43 lis broken. Consequently, the high,

pass filter 1,1 atthe called station remains connected to the-transmitting channel and the low pass filter 12 remains connected to the receiving channel. The generator 7 oseillates at the higher carrier frequency f2 and sends to theline a continuous' train of oscillations through the hi h pass filter 11,. The operal tors or subscri ers may now converse with each other inasmuch as at each station the outgoing oscillations will be modulated in accordance with speech and the incoming oscillations will be detected bythe detector 16 and impressed upon the telephone circuit. `The called station always transmits on the higher of the two carrier frequencies and receives on the lower. K

Operation zt an, alle statiomlVhcn oscil- 5 lations of the frequency f1 are impressed upon the line, the relays 42, 43 and 44 are actuated once for each group of impulses. However, if the spacingof the impulses is not that for which the selector 17 is set, the selector 17 does not close the circuit of the bell 18, but, at the cessation of the incoming impulses, the selector returns to its normal position. Each impulse ofcurrent of the frequency f1 will aetuatethe relays 42 and 43 as stated beavoid interfering with conversations in progf ress.

Emergency cey operation-If line conditionsare too abnormal to allow code selective ringing,if the selector circuits are not operating properly, if there are only two stations upon the line, or, if it is desired to arrange so that all the stations may be called simultaneouslyfrom a` chief operators or dispatchers station, the key 46 may be operated. High frequency impulses put upon the line will then cause the relay ldirectly through the bell 18. If continuous oscillations are put upon the line, the bell 18 at each station where key 46 is operated will ring continuously or any predetermined code of ringing may be employed. The selector keys SK in this case are employed to transmit impulses or a hand key may be used in place of the selector keys in a manner which will be obvious. It is customary in connection with the use of selectors such as the selector 17 to provide one selector key lSK at a chief dispatchers office with an arrangement of teeth adapted to call all the stations upon the line simultaneously. This mode of-operation may be employed in the present instance, if. for example, an emergency renders it necessary for the dispatcher to give directions to attendants at all the stations simultaneously.

Automatic gain control operation- In the anode-cathode circuit of the detector tube 16,

43 to close acircuit is connected a resistance 47. The space cur- I ance. The grids of the tubes of are normally polarized by a source 48.

. When normal stren h waves are coming in,

the additional polarizing potential dueto the drop across the resistance 47 -just suiiices for,

' the received waves. The grid o tube 16 `may also be connected to the same terminal of the i battery 48 to which the grids of the amplifier tubes 15 are connected. 'l -Also the grid of tube 16 may alone be thus'connected and the grids of tubes 15 may be connected to ground through an invariable biasing battery. Condensers 49 and resistance 56 serve as a grid circuit filter and serve the double purpose of shunting speech'frequency variations around the resistance 47 and preventing the ampliier 15 and detector circuit 16-fromacting as an oscillationgenerator because any oscillations generated in the plate circuit of the tube 16 whichtend to be fed back to the grid circuits of the` ampliiierare largely shunted through the combination of resistance 50 and capacities 49. A condenser 59 bypasses car-- rier frequency waves around the relay 42..

Auxiliary amplifier ciraz't operatz'onf-If line conditions are bad owing to a breakin the line or a section of the line being down, the switch 51 is moved from the normal down position to the up position, thus connecting a power source 52 to the motor generator 53 and energizing the plate and lament circuits of the Vpower amplifier 10. The outgoing channel will then extend from the cuit of the amplifier 9 through the 'gh 4frequency transformer 54 to the grid circuit of the amplifier 10 and from the plate circuit of Vthe amplifier 10 through the high frequency transformer 55 and the high or low pass filter 11 or 12,^`as the case may be, to the line. v The tube 10 is a tube amplier of considerable output, capable of supplying from ve to twenty times more energy than the power normally used for transmitting.

It is contemplated that the coupling circuit 13 should have the transmission characteris-A tic of a very flatly tuned circuitor preferably that it should have the characteristic of a band pass filter, thus transmitting with negligible attentuation currents of frequencies of 80,000 and 100,000 cycles per second or whateverfrequencies are used in the particular system. Such a band filter characteristic may be obtained by properly choosing the capacities 19 and 21, inductances 20, 22 and 23, and the capacities 14. If the signaling circuit side of the capacities 14 has a capacity to ground this must also be Ytaken into account in designing.

Fig. 2 shows apparatus for connecting the late cir- 3. This apparatus corresponds to and may be fused in lieu of the capacities 1'4 inthe circuit of Fi 1. The aerials 63 are mounted upon suitab e supports 64 'and connected 'with the ,two conductors of the power line3 which are to be used for transmission. I When the power the amplifier signaling circuit to the power line conductors line 3 consists of several multiphase conductors any twovconductors may be selected as signaling conductors. Thek aerials 63 are at the potential of the power line conductors to which they are connected and are insulated by suitable high voltage insulators 65. Adjacent to each antenna@ is an aerial 66 which may comprise a plurality of sections, preferably two, as illustrated in Fig. 2, located one upon each side on the antenna 63 and equidistant therefrom. Each pair of aerials 66 is connected by suitable leads 67 to the signaling apparatus through the coupling circuit 13.

The antenna or aerial condenser described may be located either'in a horizontal or a vvertical plane. That is, the antennae 66 may be respectively above and below the antenna 63. or may beV positioned at the sidesothereof. This coupling arrangement has numerous advantages. A suiiiciently large capacity to connect the power line and the signaling apparatus is readily attained. The supports 64 and theV aerials 63 and 66 maybe constructed vin a manner to withstand eXtreme weather :conditions and thus avoid danger of direct conductive contact between the signaling circuit and the power line even ifl that portion of Ythe power line immediately adjacent the antenna structure should break and fall to the ground. The respective conductors 3 of the transmission circuit act i'n'series to form a path in shunt across the power line terminals of the coupling circuit 13. It is accordingly very difcult to predetermine the characteristics of this termination since the capacities from the conductors 3 to ground are determined primarily by the power lines and are not readily subject to control or variation to meet the requirements of the signaling circuit. ln the case of the separate capacity coupling structure illustrated in Fig. v2, however, itis possible to redetermine the capacity between the aeria 63 and ground and to design the coupling circuit 13 accordingly.

Fig. 3 illustratesa battery of two 'coupling i condensers 70 of another type, each of which comprises a metal tank 71 filled with oil to a suitable level, as at 72, and mounted'onhigh tension insulators 73 on a base 74 of concrete or like material. These condensers operate at extremely high voltages and, although the tank 71 is at relatively low voltage with respect to ground, it is desirable in the interests of safety to surround the battery -of conf densers with a guard rail or equivalent device 75. The condenser comprises, in addition to the container 71 which serves as a low potential plate, a hollow interior member 76, lixedly supported within the cont/einer 71 by means of the lower supporting'member 77 which -may be in the form of a ltripod formed of'insulat-I to the lower portion of the tank. To `permit of necessary expansion and contraction with-- in the tank, a vent member 81 which is so designed as not to admit rain orv snow is connected through the upper` portion of a cap' member of the tank. Theinterior plate 7 6 is preferably formed of a cylinder to which are soldered or welded hemispherical ends. ,In order to-avoid any fringing or brush discharge, the interior surface of the tank 7 1 and the exterior surface of the interior plate 76 are made as smooth as possible. The interior plate 76 may, for example, be joined to the lemispherical portion by a butt joint, in order to avoid sharp Vedges and rough surfaces. In such casesan overlapping ring 82 within the member 7 6 may be used to reinforce the joint. This construction enables the high tension electrostatic condenser to be built with the requisite capacity and without employment of a very large ,quantity of oil or other dielectric. It will be understood that the two condensers of the battery 17 may be employed to replace the two condensers illustrated in Fig. 2, the connections 79 from the respective condensers leading to the high power transmission conductors 3, and the low tension terminals 83 leading to the signal coupling circuit 13.

Fig. 4 illustrates a modified form ofl oil dielectric Vcondenser provided with a plurality of plates. As in the apparatus of Fig. 3, the low tension plate of the condenser' comprises an oil-filled container 84. The high tension plate 85, connected to the power line by lea'd 7 9 extending through the high tension insulating bushing 78, is similar to the high tension plate 76 of thevcondenser of Fig. 3. Placed within the tank 84 and surrounding the plate 85 are a number of centrally aligned tubular plates suitably spaced from each other and supported at their lower ends by a series of insulating supports 86. These plates are alternately' connected to the tank 84 and the high tension plate 85 and thus serve with the plates 84 and 85 to con-l stitute a multi-plate condenser. The connecting members 86 which serve to electrically connect the high tension plates to each other andthe low tension plates to each other are,`in effect, also supporting brackets, and support the high tension plates from the inner plate 85 and the low tension plates from a ledge on the inner wall of the low'tension plate or tank 84. In order to permit circulameassa tion of the oil around and through the tubular plates ,and to permit accumulations of water and sediment tobe withdrawn, each of the tubular plates is provided with a drainage I aperture 87 through which the heavier vmaterial may pass toward the bottom of the tank A84. In this apparatus, as in that of Fig. 3, the oil level is preferably kept to a point above the exposed surface of the interior high tension plate. Moreover, in both designs, the surfaces .from which Stringing is apt to occur are curved and so shaped ,as to avoid'sharp angles'and points'. l

In Fig. 5, there is .disclosed an arrangement consisting of an exterior sphere 90 and an interior sphere 91. The space between the two spheres is filled with oil or other suitable dielectric. The outer member 90 is preferably formed of two hemispheres, bolted, or otherwise'suitably secured together in such manner as to present a smooth interior surface. The outer shell is also pro-v lvided with the usual drainpipe'SO and a low tension. connecting lead 92'. The entire structure is supported from a high tension insulating bushing 93 which extends through the upper portion of the outer sphere 90 and serves not only to effectively Vinsulate the connecting lead 7 9but also as a mechanical support for the interior sphere as well. This insulator is 'supported directly from the power conductor 3,-preferably at a point just beneath and in line with a suspension insulator 94 which serves to support the power conductors 3 thus transferring the mechani-V 'cal strain directly to the transmission line tower. This structure has the advantage that for a given electrostatic capacity, a minimum quantity of oil or dielectric, is required.

In the modification of Fig. 6, the condenser consists of two tubular members 95 and 96, the outer of which serves as the high tension plate and is directly connected to the high tension transmission conductor 3. The interior plate 96 is held in position within the exterior plate by means of a spacing insulating support 97 and the high tension insulator 98. The low tension. conductor 99 is, in this instance, insulated from the high tension plate by means of the insulator 98 and is electrically connected directly to the low tension plate 96. Inasmuch as the high' tension platel 95 substantially completely shields the low tension plate 96, the resulting capacity to ground from this structure is very small.

Certain features of the system herein described are disclosed and claimed in the copen'ding application of V. Wolfe, Serial No. 664,147 filed simultaneously herewith.

Obviously many of the features of this invention are applicable to signaling systems generally and it is therefore to be understood that the invention is not to be limited to the systems disclosed.

What is claimed is: ber and order oimpulses or" current of a r6- l. In a system for signaling, a high voltdetermined frequency, means at the calling age transmission line, a plurality of stations connected to said line and each having high frequency transmission and high frequency reception apparatus, means at at least one station to selectively call any other station` and communicate therewith telephonically with waves or apredetermined frequency, and means at an idle station actuatedby calling or telephone currents to indicate that" the signaling circuit is busy.'

2. In a system for communicating by carrier waves, a high voltage transmission line, a plurality of stations connected to said line, means whereby each station is normally conditioned for the reception of a call on a Wave of one frequency, means whereby any station calling transmits Waves over said transmission line of that frequency for calling and telephoning, and means at an idle station whereby waves of that frequency indicate that the signaling system is busy.

3. In a carrier wave communication system, means comprising altransmitting key for sending group'sof waves' of a predetermined frequency to the medium connectlng the stations 1n predetermined number and order, a

selective deviceat a station to be selected responsive only to the currents corresponding to predetermined number and order of impulses for operatively aecting the circuit of an indicating device, and a circuit varying device which upon being operated, connects the indicating device in circuit to be operated directly as a result of the operation of the transmitting key without the actuation of a selective device.

i. Apparatus for connecting a signaling circuit to power line conductors for full metallic circuit communication over the power line conductors comprising an aerial connected to each of the conductors, means :tor supporting said aerials at a point away from the power line, saidV aerials being supported independently of they power line conductors, and other aerials supported adjacent to the tem, a plurality of stations, medium connecting said stations, a transmitting key at at least one station for sending predetermined high fre- -quency 1n predetermined number and order station for effecting telephone communication with the called station using said wave cipredetermined frequency as a carrier, and means at each idle station controlled by calling telephone current from the calling station to indicate that the 'circuit is busy.

7. In a carrier wave communication sysa transmitting groups of Waves of a to the medlum connecting the stations, a selective device at each station responsive only to a predetermined number and order of impulses or operatively affecting the `circuit of an indicating device, means at the calling station for eecting telephone communication with the called station using said predetermined frequency as a carrier Wave, and means at each idle station controlled by calling or telephone current from the calling station to indicate that the circuit is busy.

In witness whereof, I hereunto subscribe myname this 23 day of September A. D.,

PORTER H. EVANS.

iirst-named aerials respectively and connected to the terminals of the signaling circuit to effect a capacity connection between the sigmaling circuit and the power line. l l

5; A capacity deyice for connecting a power line and signaling apparatus comprising an elevated structure located at a point away .from the power line, parallel aerials supported thereby independently of the power line, one of said ,aerials being electrically connected to said'power line, and another o'f said aerials being electrically connected to said signaling apparatus.

' 6. In a system-for communication overA a power line, a high voltage transmissioniline, aplurality of stations connected to 'said line, means vat each station for selectively calling `anyother station by a predetermined num- 

